The purpose of this study is to investigate a new blood pressure lowering drug. This drug, irbesartan, is a member of a new class of antihypertensive agents which inhibit the renin angiotensin system by blocking the effect of a hormone, angiotensin II. It is hoped that irbesartan, which specifically inhibits the effect of angiotensin will allow blood pressure lowering without contributing to other important side effects, in particular kidney damage to patients with Diabetes Mellitus.